The invention relates to a device for inspecting the upper surfaces of successive objects, for instance the mouth edges of glass bottles carried by a conveyor belt and guided thereby past the device, which device is provided with an optical system, comprising:
a lighting system with a light source for lighting an upper surface of each object, and
an optical imaging system for forming in each case an image of an upper surface.
Such a device is known in diverse embodiments. The articles for inspection, for example glass bottles, may, as a result of the nature of the production process, have mutual height differences. These height differences can cause problems with respect to the automatic visual inspection of the bottle mouth. A bottle inspection device is known for instance in which the height difference is levelled out by grasping each bottle under the flanged edge or neck that protrudes sideways at the top. Small differences in height can be evened out in this way.
If the height differences are not evened out or are inadequately evened out, the optical path length from the light source to the image of the upper edge will not be the same for each bottle. As a result, the setting of an inspection system cannot be carried out optimally. A consequence of this positional inaccuracy is that accuracy of inspection has to be sacrificed.
The invention has for its object to embody a device of the type described such that the above stated problem is solved.
The invention also aims to embody a device of the noted type such that it can be added to an existing conveyor device, for instance a bottle conveyor.
A further object of the invention is to provide a device which enables a very compact construction.
Finally, the invention aims to embody an inspection device such that great flexibility is achieved, and such that it always operates reliably, irrespective of the mutual interval between the objects.
Generally, the invention provides a device of the above described type that is characterized by:
measuring means for measuring the height of one edge at a time, and
adjustment means for setting the optical system on the basis of the height of an edge as determined by the measuring means.
A very simple embodiment is one in which the adjustment means comprise an optical element displaceable along the optical axis. Such an optical element can be given a lighter form than a light source and is moreover a passive element so that difficulties with cables are not encountered.
In a very simple embodiment the optical element comprises a lens.
In order to obtain an intensive lighting for the inspection of bottle mouths or other annular reflecting surfaces, use is preferably made of a ring-shaped light source. Such a light source is per se known, for instance in the form of annularly arranged outer ends of light conductors coupled to a light source.
Preference is given, however, within the scope of the invention to an embodiment of the lighting system that not only functions as ring-shaped light source but also emits as much directed light as possible to the annular surface for inspection, this in order to prevent masking of faults, which can occur in the case of radiation with non-directed light. In this respect the invention provides a device displaying the feature that the optical element comprises a transparent block, which block
is cylinder-shaped,
has an entry surface facing the light source,
comprises a conical hollow, the top of which is directed to the entry surface, and
has an exit surface extending in the form of a ring between the base of the hollow and the cylinder surface. In this embodiment the block functions as light conductor, as a result of which the light falling in on the entry surface is generated with very high yield via the exit surface.
In order to prevent undesired exit of light via the cylinder surface and/or the cone surface an embodiment can be used in which the cylinder surface and/or the cone surface is provided with a mirror.
If desired the block can be embodied such that the exit surface is diffusely transparent, for example is matted or provided with an opal covering layer. Using such an embodiment the directional preference of the outgoing light, if any, is reduced to negligible proportions.
In order to avoid spurious light possibly being generated via the cone surface an embodiment can serve in which a screen not allowing passage of light is situated in the base of the cone. The block can in this case be embodied such that a fastening member is fixed in position in the block through the top of the cone.
In a very simple embodiment the optical element comprise a lens. This lens may be an objective lens of a video camera for instance so that in accordance with the invention, focussing of the camera takes place on the basis of the measured height of the surface for measuring.
In order to obtain the best possible image of the surface for inspection, the variant is recommended in which the lighting system is arranged for emitting a light bundle concentrated on the surface for lighting. In particular the device can in this case be characterized by a ring-shaped mirror adapted to the shape of the surface for illumination, which mirror concentrates light coming from the light source on the upper surface for illumination.
For the inspection of an annular upper surface of objects, in particular the round mouths of bottles, the device can in this latter case display the feature that the ring-shaped mirror possesses the form of the surface of a frustum cone, the centre line of which coincides with the optical axis of the lighting system.
In a practical embodiment the device has the feature that the measuring means comprise a row of photo-cells. This row of photo-cells can form part of a linear-array camera.
The invention further relates to a transparent block, as specified in the foregoing. This block can serve as light conductor for the concentrating of light concentrated on the entry surface onto the ring-shaped exit surface.